Intervertebral Implant Facilitating Unilateral Placement, Instruments and Methods

ABSTRACT

Implants, tools and methods for performing unilateral posterior lumbar interbody fusion are provided. An interbody implant includes a body having a top and bottom surface extending along a length thereof; and first and second side surfaces extending between the top and bottom surfaces on opposite sides of the body. The height of the first side surface is greater than the height of the second side surface.

BACKGROUND OF THE INVENTION

Back pain can be caused by a variety of factors, including, but notlimited to the rupture or degeneration of one or more intervertebraldiscs due to degenerative disk disease, spondylolisthesis, deformativedisorders, trauma, tumors and the like. In such causes, pain typicallyresults from compression or irritation of spinal nerve roots by reducedspacing between adjacent vertebrae, a damaged disk and/or misalignmentof the spine resulting of the injury or degeneration.

Common forms of treating such pain include various types of surgicalprocedures in which a damaged disk may be partially or totally excised,and one or more implants is inserted between adjacent vertebrae in aneffort to restore the natural spacing and alignment between thevertebrae that existed previous to the injury or degeneration, so as torelieve the compression, irritation or pressure on the spinal nerve ornerves and thereby eliminate or significantly reduce the pain that thepatient is experiencing. Typically, the one or more implants are usedtogether with substances to encourage bone ingrowth to facilitate fusionbetween the adjacent vertebrae. Some procedures provide implants thatallow at least some limited motion between the adjacent vertebrae, evenafter opposite ends of the implant are fixed to the adjacent vertebrae,respectively.

Among know procedures for performing fusion are PLIF (posterior lumbarinterbody fusion), ALIF (anterior lumbar interbody fusion) and TLIF(transverse or transforaminal lumbar interbody fusion). A PLIF procedureachieves spinal fusion in the low back by inserting an implant such as acage and, typically, graft material (to encourage bone ingrowth)directly into the disc space between adjacent vertebrae. The surgicalapproach for PLIF is from the back of the patient, posterior to thespinal column.

An ALIF procedure is similar to the PLIF procedure), except that in theALIF procedure, the disc space is fused by approaching the spine throughthe abdomen, from an anterior approach, instead of through the lowerback, from a posterior approach. Although previously there was a lot ofinterest in perfecting an endoscopic approach for ALIF surgery, it haslargely been abandoned because it placed the great vessels (aorta andvena cava) at too great a risk.

A TLIF procedure involves a posterior and lateral approach to the discspace. To gain access to the disc space, the facet joint may be removedwhereby access is gained via the nerve foramen. Typically only a singleimplant is placed in a TLIF procedure. The implant is inserted from apostero-lateral approach, as noted, and is ultimately placed in themiddle-to-anterior aspect of the disc space.

There are certain conditions where a unilateral PLIF procedure issuperior to a TLIF procedure. Such conditions include those where severspinal stenosis is present. PLIF procedures typically place a pair ofimplants, one on each side of the disc space. To accomplish this, atypical approach forms two access ports into the disc space, bothposterior to the spinal column, with one port one side relative tomidline (the spinal process) and the other on the opposite side,relative to midline. Using this approach, each implant can be deliveredand placed along a substantially direct delivery pathway. However,because two ports are formed, this results in a relatively large amountof removal of tissues, and risks nerve damage on both sides of thespinal column.

Alternatively, both implants may be delivered using a unilateral PLIFtechnique in which only one port is formed on one side of the midline,posterior spinal column. This significantly reduces the amount oftissues that need to be removed and reduces the number of nerves at riskof being damaged by the procedure by half. A unilateral PLIF procedurerequires the first implant, after being inserted into the disc space, tobe laterally driven over the midline of the intervertebral disc spaceand into position in the opposite side of the disc space. Drawbacks tocurrent procedures include difficulties in laterally driving the firstimplant from one side of the disc space to the other. During thisprocess, when using an implant/cage that has substantially equal heightson both sides of the implant/cage the leading side of the implant oftenresists moving in the transverse direction towards the opposite side ofthe disc space, and may dig into the annulus fibrosus and resisttransverse driving of the implant. Moreover, the use of standardinstruments such as cage inserters, end impactors, curved curettes,curved chisels, etc. often result in breaking the implant, when used totry to drive the implant from one side of the disc space to the other.This poses a serious risk of nerve root injury and/or injury to otherbody structures when an instrument breaks or a cage breaks, or duringthe process of removing a broken cage. Additionally, there are caseswere a broken cage is unable to be completely removed and thiscompromises a successful fusion outcome.

The use of two implants in a PLIF procedure as opposed to the use of oneimplant, such as in a TLIF procedure, has been noted to markedly improveinterbody fusion. However, it would be further advantageous to fusionresulting from a two implant procedure if the implants could be furtherlaterally spaced from the midline of the intervertebral disc space,compared to current two implant procedures, as this would furtherenhance a honeycomb formation of fusion.

There is a continuing need for implants, instruments and procedures forperforming unilateral PLIF to facilitate safer and easier delivery ofthe first implant form one side of the disc space to the opposite side.There is a continuing need to implants instruments and proceduresdesigned to permit placement of the implants further laterally from themidline of the intervertebral space than is possible using currentimplants, tools and procedures. The present invention meets at least allof the above needs.

SUMMARY OF THE INVENTION

In one aspect of the present invention an interbody implant includes animplant body having a top and bottom surface extending along a length ofthe body and also defining a width of the body; and first and secondside surfaces extending between the top and bottom surfaces on oppositesides of the body, the first side surface defining a first height andthe second side surface defining a second height; wherein the firstheight is greater than the second height. In at least one embodiment,the first height is greater than the second height by a difference inthe range of about 1.8 mm to about 2.2 mm.

In at least one embodiment, an average height of the first side surfaceover a length from a distal end to a proximal end of the body is greaterthan an average height of the second side surface over the length fromthe distal end to the proximal end.

In at least one embodiment, the first height, measured at a particularlocation along the length of the body is greater than the second height,measured at the particular location along the length.

In at least one embodiment, the first height is greater than the secondheight at all corresponding locations along the length of the body.

In at least one embodiment, the body is substantially trapezoidal-shapedin a cross section taken normal to a longitudinal axis of the body.

In at least one embodiment, the top and bottom surfaces are radiused tojoin the second side surface having a lower height than the first sidesurface.

In at least one embodiment, the first and second side surfaces aresubstantially planar and flat.

In at least one embodiment, a series of retropulsion resistors areprovided on the top and bottom surfaces, adjacent the first and secondside surfaces, with each of the retropulsion resistors being configuredto prevent retropulsion of the implant out of the interbody space.

In at least one embodiment, the retropulsion resistors comprise teethconfigured to resist movement of the body out of the interbody space.

In at least one embodiment, at least portions of the top and bottomsurfaces are convexly curved in a direction along a longitudinal axis ofthe body.

In another aspect of the present invention, an instrument for driving aninterbody implant is provided that includes: a rigid elongated shafthaving proximal and distal end portions; a handle formed at the proximalend portion; and a working end formed at a distal end of the instrumentand extending from the distal end portion, the working end including afirst member and a second member, the first member being longer than thesecond member, the first member forming a first angle with alongitudinal axis of the instrument and the second member forming asecond angle with the longitudinal axis.

In at least one embodiment, the first member is a first foot and thesecond member is a second foot, the first and second angles openingtoward a distal direction, and the first angle being smaller than thesecond angle.

In at least one embodiment, the first member and the second member formsubstantially a right angle therebetween.

In at least one embodiment, the first angle is in the range of abouttwenty degrees to forty degrees and the second angle is in the range ofabout fifty degrees to about seventy degrees.

In at least one embodiment, the first angle is about thirty degrees andthe second angle is about sixty degrees.

In at least one embodiment, the first member is a foot and the secondmember is a knob configured to be received through a side opening of theinterbody implant, the first and second angles opening toward a distaldirection.

In at least one embodiment, the first angle is in the range of aboutthirty degrees to about sixty degrees and the second angle is in therange of about thirty degrees to about fifty degrees.

In at least one embodiment, the first angle is about forty degrees andthe second angle is about fifty degrees.

In another aspect of the present invention, an interbody implant systemis provided that includes: an interbody implant including an implantbody having a top and bottom surface extending along a length of thebody and also defining a width of the body; and first and second sidesurfaces extending between the top and bottom surfaces on opposite sidesof the body, the first side surface defining a first height and thesecond side surface defining a second height; wherein the first heightis greater than the second height; and an instrument for driving theinterbody implant, the instrument including: a rigid elongated shafthaving proximal and distal end portions; a handle formed at the proximalend portion; and a working end formed at a distal end of the instrumentand extending from the distal end portion, the working end including afirst member and a second member, the first member being longer than thesecond member, the first member forming a first angle with alongitudinal axis of the instrument and the second member forming asecond angle with the longitudinal axis.

In at least one embodiment, the system includes a pair of the interbodyimplants.

In at least one embodiment, the instrument is a first instrument, thefirst member is a first foot and the second member is a second foot, thefirst and second angles opening toward a distal direction, and the firstangle being smaller than the second angle; the system further comprisesa second instrument, the second instrument including a second rigidelongated shaft having proximal and distal end portions; a second handleformed at the proximal end portion of the second shaft; and a secondworking end formed at a distal end of the second instrument andextending from the distal end portion of the second shaft, the secondworking end including a foot member and a knob, the foot member beinglonger than the knob, the foot member forming a third angle with alongitudinal axis of the second instrument and the knob forming a fourthangle with the longitudinal axis of the second instrument.

In another aspect of the present invention, a unilateral method ofinserting first and second interbody implants is provided, the methodincluding: creating an interbody port on one side of the spinal column,while maintaining structures of the spinal column and the lumbarmusculoligamentous complex on an opposite side of the spinal columnrelative to the port, intact; removing disc material through an incisionin an annulus fibrosus of a disc in communication with the port andthrough the port; inserting the first interbody implant through the portand into the disc space, wherein the first interbody implant has a firstdistal end portion, a first proximal end portion and first and secondsides extending between the first distal end portion and the firstproximal end portion, wherein a height of the first interbody implant onthe first side is less than a height of the interbody implant on thesecond side, and wherein the first interbody implant is inserted suchthat the first side is medially placed and the second side is laterallyplaced on a first side of the disc space; driving the first interbodyimplant from a location in the disc space on the first side, over themedian of the disc space and into a position in the disc space on asecond side of the disc space, such that, as a result, the first side islaterally placed and the second side is medially placed on the secondside of the disc; and inserting the second interbody implant through theport and into the disc space on the first side of the disc space,wherein the second interbody implant has a second distal end portion, asecond proximal end portion and third and fourth sides extending betweenthe second distal end portion and the second proximal end portion,wherein a height of the second interbody implant on the third side isless than a height of the second interbody implant on the fourth side,and wherein the second interbody implant is inserted such that thefourth side is medially placed and the third side is laterally placed ona first side of the disc space.

In at least one embodiment, the first and second interbody implants areeach substantially trapezoidal-shaped in a cross section taken normal toa longitudinal axis thereof.

In at least one embodiment, the method includes distracting the discspace prior to the inserting steps, by applying distraction forces tovertebrae adjacent the disc space.

In at least one embodiment, the method includes packing each interbodyimplant, prior to the inserting, with a material that encourages boneingrowth.

In at least one embodiment, the method further includes packing a spacebetween the interbody implants, after insertion thereof, to encourage ahoneycomb pattern of bone ingrowth into the disc space.

These and other advantages and features of the invention will becomeapparent to those persons skilled in the art upon reading the details ofthe implants, systems, instruments and methods as more fully describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an implant according to an embodimentof the present invention.

FIG. 1B is a side view of the implant of FIG. 1A.

FIG. 1C is a longitudinal sectional view of the implant of FIG. 1B takenalong line 1C-1C.

FIG. 1D is a top view of the implant of FIG. 1A.

FIG. 1E is a cross-sectional view of the implant of FIG. 1D taken alongline 1E-1E.

FIG. 1F is a detail view of the portion of FIG. 1B captured by circle1F.

FIG. 2 is a perspective view of an embodiment of an inserter instrumentused for the initial insertion of an implant according to the presentinvention.

FIG. 3A is a perspective view of a first side impactor instrumentaccording to one embodiment of the present invention.

FIG. 3B is a plan view of the instrument of FIG. 3A.

FIG. 3C is another plan view of the instrument of FIG. 3A, with theinstrument having been rotated ninety degrees about its longitudinalaxis, relative to the plan view shown in FIG. 3B.

FIG. 4A is a perspective view of a second side impactor instrumentaccording to one embodiment of the present invention.

FIG. 4B is a plan view of the instrument of FIG. 4A.

FIG. 4C is an enlarged view of the portion of the instrument shown inFIG. 4B within circle 4C.

FIG. 4D is another plan view of the instrument of FIG. 4A, with theinstrument having been rotated ninety degrees about its longitudinalaxis, relative to the plan view shown in FIG. 4B.

FIGS. 5A-5E illustrate a method of inserting a pair of implants using aunilateral PLIF method according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present implants, instruments and methods are described, itis to be understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned herein areincorporated herein by reference to disclose and describe the methodsand/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “animplant includes a plurality of such implants and reference to “thenerve” includes reference to one or more nerves and equivalents thereofknown to those skilled in the art, and so forth.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

DEFINITIONS

A “retropulsion resistor” is a feature configured to resist backing outof the implant once it has been finally placed, as well as at anylocation along its delivery pathway. One or more repulsion resistors maybe formed in or on an implant, preferably in or on both top and bottomsurfaces of the implant.

A “tooth” as defined herein, refers to a feature having a peak such asan edge designed to function as a retropulsion resistor. For example aseries of teeth may be provided to form a sawtooth-like pattern so as toresist retropulsion. In a preferred embodiment, the sides of the teethare symmetrical. Alternatively, the sides may be asymmetrical, forming a“shark-tooth pattern”, wherein the apex of the tooth is biased eithertoward the distal end portion of the implant or proximal end portion ofthe implant, preferably toward the distal end portion.

“Honeycomb grafting” refers to a technique in which graft material (e.g.autograft or allograft cancellous bone) is laid down in a graft site toform a network of interstice containing hematipoietic elements, whereinthe interstices are arranged in a honeycomb like network formation. Thehoneycombed network enhances the osteoinductive, osteogenic andosteoconductive properties of the bone grafted as well as the chance ofobtaining a fully integrated region of new bone.

Referring now to the drawings in detail, FIGS. 1A-1B show a perspectiveview and a side view, respectively, of an implant 10 according to anembodiment of the present invention. FIG. 1C is a longitudinal sectionalview of FIG. 1B taken along line 1C-1C. FIG. 1D is a top view of theimplant 10 of FIG. 1A and FIG. 1E is a cross sectional view of FIG. 1Dtaken along line 1E-1E.

Implant 10 is formed of a unitary body having a length 12 (see FIG.113), width dimension 14 (see FIG. 1E) and height dimension 16 (see FIG.1E). 1. The body includes a top surface 10T and a bottom surface 10Bextending along the length 12 of the implant 10 and also defining thewidth of the implant body. The top and bottom surfaces 10B, 10T may bemirror images of one another, as illustrated in FIG. 1B.

First and second side surfaces 10S1 and 10S2 extend between the top 10Tand bottom 10B surfaces on opposite sides of the implant 10 body. Thefirst side surface 10S1 defines a first height 16S1 and the second sidesurface 10S2 defines a second height 16S2. The first height 1651 isgreater than the second height 16S2 by a predefined amount.

In the embodiment of FIG. 1E, the implant body is radiused or otherwisetapered in a direction extending from the midline along the longitudinalaxis L-L thereof toward the second side surface 10S2. Thus, top andbottom surfaces 10T and 10B are tapered or beveled as illustrated inFIG. 1E, starting from a height (separation distance of top and bottomsurfaces) of 16S1, down to a height (separation between top and bottomsurfaces) of 16S2, as shown in FIG. 1E. The embodiment of FIGS. 1A-1E inthis way provides a body that is substantially trapezoidal-shaped in across section taken normal to a longitudinal axis of the body, asillustrated in FIG. 1E. Variations of the cross-section shown in FIG. 1Einclude those in which the shape of the top 10T and/or bottom 10Bsurfaces are curved or straight. When straight, they may have the sameor different inclinations. When curved, they may have the same ordifferent radii of curvature.

In general, by providing an implant body that has a first side 10S1 thathas a height 16S1 that is substantially greater than a height 16S2, ofan opposite side (second side) 10S2, whether the cross-section shape istrapezoidal or some other shape, the tapered shape of the implant topand bottom surfaces 10T, 10B joining the second side 10S2 facilitatesdriving the implant 10 laterally with the side 10S2 having reducedheight 16S2 being the leading side of the implant during lateraldriving. This helps prevent snagging, catching or digging in of theimplant side 10S2. This also allows the implant to be driven furtherlaterally than what is possible when using an implant that has asubstantially square or substantially rectangular cross-section, whereboth sides have the same height, because of the biconcave shape of thedisc space. The ability to place the implants further laterally relativeto the midline of the disc space allows relatively more bone graft to beplaced in between (medial of) the two implants, which greatly enhancesthe ability to achieve a desired “honeycomb” pattern of grafting,resulting in the achievement of a superior fusion. Additionally, byproviding an implant body that has a first side 10S1 that has a height16S1 that is substantially greater than a height 16S2, of an oppositeside (second side) 10S2, this reduces the amount of lateral force thatneeds to be applied to the implant to drive it laterally from one sideof the disc space to the other, relative to the amount of force that isneeded to drive an implant having first and second sides ofsubstantially equally height. Accordingly, this design of the implantreduces the risk of breaking the implant 10 during lateral driving, asrelatively less lateral force needs to be applied to drive the implant10 laterally as described.

In at least one embodiment, the height 16S1 is greater than the secondheight 16S2 by a difference in the range of about 1.8 mm to about 2.2mm. In at least one embodiment, the average height of the first sidesurface 10S1 over a length from a distal end to a proximal end of theimplant 10 body is greater than the average height of the second sidesurface 10S2 over the length from the distal end 10D to the proximal end10P. Preferably the first height 16S1, measured at any particularlocation along the length 12 of the first side 10S1 is greater than theheight 16S2 of the second side 10S2, measured at the same location alongthe length 12 on the second side 10S2. Preferably, each heightdifference between 16S1 and 16S2 at a same corresponding location alonglength 12 is in the range of about 1.8 mm to about 2.2 mm, typicallyabout 2 mm. Thus, the first height 16S1 is preferably greater than thesecond height 1652 at all corresponding locations along the length ofthe implant body.

Implant 10 is a substantially straight implant. Thus, side surfaces 10S1and 10S2 are preferably substantially aligned with the longitudinal axisL-L of the implant 10, and are substantially planar and flat. Theexception to this are the locations along the distal end portion 11D andthe proximal end portion 11P where the side surfaces 10S1 and 1052 tapertoward one another to defined the reduced widths of the proximal anddistal end portions 11P,11D, relative to the main body portion 11M.

A series of retropulsion resistors, such as teeth 20 may be formed onthe top 10T and bottom 10B surfaces, adjacent the first and second sidesurfaces, as shown in FIGS. 1A-1B, for example. The retropulsionresistors 20 are configured to prevent retropulsion of the implant 10out of the interbody space once it has been implanted there. The top andbottom surfaces 10T, 10B may be convexly curved in a direction along thelongitudinal axis L-L of the implant, which may better conform the topand bottom surfaces to the vertebrae forming the interbody disc space,as the vertebrae surfaces forming the interbody disc space are concavein the anterior-posterior direction, as well as the latero-medialdirection. The convexity of the top and bottom surfaces 10T, 10B alsoresults in reduced height of the distal and proximal portions 11D, 11Prelative to the height of the central portion 11M on the same side ofthe implant 10. This condition is true for both sides 10S1, 10S2. Thereduced height of the distal end 10D and the tapered, varying height ofthe distal end portion 11D facilitate insertion of the implant 10between adjacent vertebral bodies. The reduced height of the proximalend 10P and tapered, varying height of the proximal end portion 11Pbetter conform this portion to the shape/contours of the inter-vertebraldisk space for improved load sharing, that is with a more even loaddistribution over the length of the implant 10. Implants 10 can bemanufactured to have a variety of sizes to accommodate different sizesof patients and different inter-vertebral locations. In one non-limitingexample, implants 10 may be manufactured in lengths 12 of 22 mm, 24 mm,and 26 mm and in 1 mm height 16S1 increments from 7 min to 15 min (eachhaving the requisite height differential between height 16S1 and height16S2). The width 14 may be about 9 mm or about 10 min or in the range ofabout 9 mm to about 10 mm, although this may also vary.

The proximal end 10P of implant 10 includes a pair of slots 22 and athreaded bore 24 which facilitates positive engagement of an inserterinstrument 100 in a manner described in more detail below.

Implant 10 is formed as a cage having a unitary body, with openingsprovided through the top and bottom surfaces 10T,10B to form cavity 26,wherein the opening formed in the top surface 10T is in communicationwith the opening formed in the bottom surface 10B and is configured anddimensioned to receive graft material, such as bone particles or chips,demineralized bone matrix (DBM), paste, bone morphogenetic protein (BMP)substrates or any other bone graft expanders, or other substancesdesigned to encourage bone ingrowth into the cavity 26 to facilitate thefusion. Although shown as a single, large cavity 26, implant 10 may bealternatively configured to provide two or more cavities that extendfrom top to bottom of the implant body 10 and through top and bottomsurfaces 10T, 10B and provide the same function as cavity 26.Additionally implant 10 is provided with one or more side openings 28 asshown in FIGS. 1A-1C. In the embodiment shown, three side openings 28are provide through both sides 10S1, 10S2 and are aligned with oneanother, as shown in FIG. 1C. Side openings 28 facilitate retention ofthe graft material in a honeycomb-like configuration and also encourageingrowth or bone to form a honeycomb like capture of the implant 10.Additionally, at least one side opening 28 may function as an interfacewith a side impactor tool during lateral driving of the implant 10, asdescribed in more detail below.

Implant 10 is preferably made from PEEK (polyetheretherketone) and ispreferably machined therefrom, but alternatively, may be manufactured byinjection molding or three-dimensional lithographic printing, forexample. When manufactured by three-dimensional lithographic printing,implant 10 may be made of polymers, such as PEEK or other polymer and/orabsorbable materials such as tri-calcium phosphate (TCP), hydroxyapatite(HA) or the like. When made of metal (titanium, stainless steel or otherbiocompatible metal or metal alloy, implant 10 may be machined or madeby metal powder deposition, for example. Alternatively, implant 10 maybe made of PEKK(poly(oxy-p-phenyleneisophthaloyl-phenylene/oxy-p-phenyleneterephthaloyl-p-phenylene)or carbon-filled PEEK. Manufacturing the implant from any of thesepolymer materials makes it radiolucent, so that radiographicvisualization can be used to view through the implant 10 to track thepost-procedural results and progress of the fusion over time.Alternatively, implant 10 could be made of titanium or otherbiocompatible, radiopaque metal. However, this is less preferred as thistype of implant would obscure post-procedural radiographic monitoring.

In order to facilitate visualization of the implant 10 during theprocedure, so as to confirm that the implant is being delivered along adesirable delivery pathway and that the implant 10 is maintaining adesirable orientation, implant 10 is provided with at least threeradiopaque markers 30. In the example shown, one marker 30 is providedadjacent side 10S1 at or near the top surface 10T of the proximal endportion (FIG. 1A), a second marker 30 is provided adjacent side 10S2 ator near the bottom surface 10B of the proximal end portion (illustratedin phantom in FIG. 1D), and a third marker 30 is provided horizontally,adjacent the distal end portion (See FIG. 1A) in a location 30′ (FIG.1C) between sides 10S1 and 10S2. By placing radiopaque markers 30 asdescribed, this enables radiographic viewing of the markers 30, at anylocation along the delivery pathway and during the procedure, as well aspost-procedurally, to accurately determine the three-dimensionalpositioning of the implant 10. Thus, not only can the radiographicimaging determine the location that the implant 10 is placed in, it canalso determine the three-dimensional orientation of the implant relativeto the anatomy at the location that it is placed in.

As shown, retropulsion resistors are provided on both top and bottomsurfaces 10T, 10B along two longitudinally extending locations, as aplurality of teeth that extend adjacent sides 10S1 and 10S2. Each tooth20 angles outwardly over a direction from a most inset portion (referredto as a valley) 20V toward tip or peak 20T, as illustrated in FIG. 1F.Tooth 20 is symmetrical, such that distal side 20D of tooth 20 is ofequal length to proximal side 20P, and a line drawn through the peak 20t perpendicular to the top 10T or bottom 10B surface bisects the angleformed by the sides 20D and 20P. Alternatively, teeth 20 may be biasedtoward the distal end (or proximal end, but preferably toward the distalend) of the implant 10, such that the distal side 20D of tooth 20 isshorter (or longer) than the proximal side 20P of tooth 20. The angle 21formed by a proximal side 20P and a distal side 20D extending fromvalley 20V is about forty-five to about ninety degrees. In theembodiment shown in FIG. 1F, angle 21 is about eighty degrees. Theheight 23 of tooth 20 measured in a direction perpendicular to thelongitudinal axis L-L/top surface 10T/bottom surface 10B is about 0.5 mmto about 1.0 mm. In the embodiment shown in FIG. 1F, height 23 is about0.75 mm. Thus, the height of peak 201 above valley 20V in FIG. 1F isabout 0.75 mm, measure in the height direction perpendicular to thelongitudinal axis L-L.

Once implant 10 has been inserted and placed as desired in the discspace, and distraction is removed, teeth 20 resist movement of theimplant 10 toward the proximal direction, as the peaks 20T of the teeth20 bite into the bone/tissue and acts as an anchor or brake thatprevents the backing out or substantial proximal movement of the implant10.

FIG. 2 shows a perspective view of an inserter instrument 100 configuredand dimensioned for inserting implant 10 between adjacent vertebralbodies. Insertion instrument 100 is a straight instrument, having asubstantially straight, elongate shaft 102 having a proximal end portion104 and a distal end portion 106. The distal end portion 106 includesthe working, end of the instrument that includes a pair of posts 108,one on either side of threaded shall 110. An actuation knob 112 isprovided at the proximal end portion of instrument 100. Actuation knob112 is rotatable relative to shaft 102, but rotatably fixed relative tothreaded shaft 110. Actuation knob is rotatable around the axis of theinserter and the central shaft rotates along with it. By aligning theposts 108 with slots 22 and aligning threaded shaft 110 with threadedbore 24, actuator knob 112 can be rotated relative to shaft 102 to screwthe threaded shaft 110 into the threaded bore 24. This causes theworking end of instrument 100 to be drawn up against the proximal end10P of implant 10, including drawings the posts 108 into slots 22 suchthat the contact surface 114 of the working end abuts against theproximal end 10P of the implant as shown in FIG. 5A, with implant 10having been securely joined to instrument 100, such that implant 10 canneither translate nor rotate relative to instrument 100. To release theimplant 10, the actuation knob 112 is simply reverse-rotated untilthreaded shaft 110 separates from threaded bore 24, after whichinstrument 100 can be withdrawn without affecting the positioning ofimplant 10.

FIG. 3A is a perspective view of a first side impactor instrument 200according to an embodiment of the present invention. First side impactorinstrument 200 has a substantially straight, rigid, elongate shaft 202having a proximal end portion 204 and a distal end portion 206. Whereasinsertion instrument 100 is configured and dimensioned to insert theimplant 10 into the disc space along a substantially straight deliverypathway in a posterior to anterior direction, first side impactor 200 isconfigured to drive the implant in a lateral-medial direction from oneside of the disc space toward the other side, after the insertioninstrument 100 has been used to initially place the implant 10 on afirst side of the disc space, which is the side aligned with the portthrough which the implant 10 is introduced into the disc space. A handle208 is formed at the proximal end portion 204 of instrument 200. Handle208 hits an outside diameter that is greater than the outside diameterof shaft 202 distal to handle 208. The enlarged diameter of handle 208facilitates the manipulation of the instrument 200 by the surgeon foruse in laterally driving implant 10.

The distal end portion 206 includes a working end that includes firstand second working members 210, 212. First working member 210 is longerthat second working member 212. First working member 210 has a length210L in the range of about eighteen mm to about twenty-two mm. In theembodiment shown in FIGS. 3A-3C, first working member 210 has a length210L of about twenty mm. Second working member 212 has a length 212L inthe range of about three mm to about seven mm. In the embodiment shownin FIGS. 3A-3C, second working member 212 has a length 212L of aboutfour mm.

First working member 210 forms an angle 214 with the longitudinal axisL1-L1 of instrument 200, angle 214 opening toward the distal direction,that is in the range of about twenty degrees to about forty degrees. Inthe embodiment shown in FIG. 3B, angle 214 is about thirty degrees.Second working member 212 forms an angle 216 with the longitudinal axisL1-L1 of instrument 200, angle 216 opening toward the distal direction,that is in the range of about fifty degrees to about seventy degrees. Inthe embodiment shown in FIG. 3B, angle 214 is about sixty degrees. Thus,the angle formed between first and second working members foot 210 andfoot 212) and that opens to the distal direction is a about ninetydegrees. First and second members 210, 212 of instrument 200 are alsoreferred to as “feet” and are substantially flat plates that areconfigured to substantially conform to and engage the proximal end 10P(working member 212) and side 10S1 (the taller side is engaged byworking member 210) of implant 10, respectively. FIG. 3C is another planview of instrument 200 with the instrument 200 having been rotated byninety degrees about longitudinal axis L1-L1, relative to theorientation shown in FIG. 3B. Working members 210 and 212 aresubstantially aligned with in the plane in which the longitudinal axisL1-L1 extends in the view shown in FIG. 3C.

FIG. 4A is a perspective view of a second side impactor instrument 300according to an embodiment of the present invention. Second sideimpactor instrument 300 has a substantially straight, rigid, elongateshalt 302 having a proximal end portion 304 and a distal end portion306. Second side impactor 300 is configured and dimensioned to driveimplant 10 further across the disc space in the lateral-medial (ormedial to lateral direction, if the implant has crossed the median ofthe disc space) so as to position it in the opposite side of the discspace. Second side impactor instrument 300 is configured for use indriving the implant 10 after the first side impactor 200 has been usedto drive the implant partially across the disc space, transverse to theposterior-anterior direction. A handle 308 is formed at the proximal endportion 304 of instrument 300. Handle 308 has an outside diameter thatis greater than the outside diameter of shaft 302 distal to handle 308.The enlarged diameter of handle 308 facilitates the manipulation of theinstrument 300 by the surgeon for use in driving implant 10transversely.

The distal end portion 306 includes a working end that includes firstand second working members 310, 312. First working member 310 is longerthat second working member 312. First working member 310 has a length310L in the range of about sixteen mm to about twenty-two mm. In theembodiment shown in FIGS. 4A-4D, first working member 310 has a length310L of about eighteen mm. Second working member 312 has a workinglength 312L extending from the surface of working member 310 in therange of about 1.5 mm to about 3.5 mm. In the embodiment shown in FIGS.4-4D, second working member 312 has a working length 312L of about 2.5mm.

First working member 310 forms an angle 314 with the longitudinal axisL2-L2 of instrument 300, angle 314 opening toward the distal direction,that is in the range of about thirty degrees to about sixty degrees. Inthe embodiment shown in FIG. 4B, angle 314 is about fifty degrees.Second working member 312 forms an angle 316 with the longitudinal axisL2-L2 of instrument 300, angle 316 opening toward the distal direction,that is in the range of about thirty degrees to about fifty degrees. Inthe embodiment shown in FIGS. 3B-3C, angle 314 is about forty degrees.Thus, the angle formed between first and second working members (foot310 and knob 312) and that opens to the distal direction is a aboutninety degrees. First member 310 of instrument 300 is also referred toas foot 310. Foot 310 is a substantially flat plate except for thelocation that member 312 extends out from. Second member 312 is alsoreferred to a knob 312. Knob 312 is substantially cylindrical in theembodiment shown, and is configured to be inserted into and engage withone of openings 28 in implant 10, typically, the proximal most opening28. It should be noted here that although opening 28 and knob 312 aresubstantially circular in cross-section, that the present invention isnot limited to this configuration, as these inter-engaging componentscould be made to have any of a number of various other shapes incross-section, including, but not limited to oval, square, triangular,irregular, hexagonal, or the like. The working end of instrument 300 isconfigured to substantially conform to and engage the side 10S1 (thetaller side) of implant 10 for applying lateral force thereto. Thus,knob 312 is inserted into opening 28 and the surface of foot 310substantially conforms to and engages the surface of side 10S1.

FIG. 4C is an enlarged, detail view of the working end that better showsthe configuration of the foot 310 and knob 312, and the angles that theyare oriented at relative to the longitudinal axis L2-L2, as well as thesubstantially right angle that they form relative to one another. FIG.4D is another plan view of instrument 300 with the instrument 300 havingbeen rotated by ninety degrees about longitudinal axis L2-L2, relativeto the orientation shown in FIG. 4B. Working members 310 and 312 aresubstantially aligned in the plane in which the longitudinal axis L2-L2extends in the view shown in FIG. 4D.

FIGS. 5A-5E illustrate a method of inserting a pair of implants using aunilateral PLIF method according to an embodiment of the presentinvention. This method is performed with the patient in a position ofnatural lordosis, either in the prone position or in a “relaxed”knee-chest position. A skin incision is made posterior to the spine andlateral to the medial line for preparation of the insertion port 400.Once the insertion port 400 has been established (which can beestablished using known techniques), the disc material is removed withan instrument such as a bone curette, by insertion of the curettethrough the port (the window into the foramen), and an incision in theannulus fibrosus. At least the anterior and lateral walls of the annulusfibrosus are preferably preserved as much as possible to provideadditional support for the implants 10.

The cartilaginous layers on the surfaces of the vertebral endplates areremoved, using an instrument such as a bone rasp, until bleeding isattained. Sufficient cleaning of the endplates is decisive for vascularsupply of the bone graft. However, excessive cleaning risks damaging thedenser bone layer and weakening the endplate, so care should be takennot to excessively remove the cartilaginous tissues.

Next, a first implant 10 is prepared for insertion. First implant 10 isfixed to inserter instrument 100 by operating actuation knob 112 toscrew threaded shaft 110 into threaded bore 24 and drawing posts 108into slots 22 in a manner described above. The hollow spaces defined byopenings 26, 28 are then filled with graft material 402. In oneparticular embodiment, graft material 402 is autologous bone harvested,for example, from the iliac crest of the patient. However, any of theother alternative materials described above could be substituted for useas graft material 402 to fill the cavities in the implant 10. The secondimplant 10 can likewise be filled at this time (before or afterattachment to a second inserter instrument 100. Additionally, graftmaterial can be tilled into the anterior portion of the disc space 406and a portion of the side of the disc space opposite of the side intowhich the port 400 enters, prior to insertion of the first implant 10.The vertebrae adjacent (superior and inferior to, respectively) to thedisc space 406 are distracted to provide additional working spacetherebetween, and allow a temporary increase in the disc space 406.

After preparation as described above, the first implant 10 is inserted,using inserter instrument 100 as illustrated in FIG. 5A. Prior toinsertion, it must be confirmed that the side 10S2 having relativelyless height is oriented so that it is facing the disc space. Thisorientation is required to facilitate transverse driving of the implant10, as during such driving, the shorter, tapered side 10S2 reduces thefriction generated, compared to a symmetrical cage where such leadingside is not tapered and is of equal height to the trailing side. Also,since the side 10S2 is tapered at both top and bottom where it joins thetop 10T and bottom 10B surfaces, this greatly reduces the risk that theside 10S2 will catch or snag on tissue as it is advanced transversely.In turn, these advantages also reduce the amount of transverse forcethat is required to be applied to side 10S1 in order to mover theimplant transversely, thereby greatly reducing the risk of breaking theimplant body 10, particularly when it is made of polymer.

Once the first implant 10 has been inserted substantially straightthrough the port 400, in a substantially posterior to anterior directionand orientation, as shown in FIG. 5A, the inserter instrument 100 isdetached from the first implant 10 by unscrewing the threaded rod 110from the threaded bore 24 (using actuator 112) and withdrawing theinserter instrument from the surgical space.

Next, the working end of first side impactor instrument 200 is insertedthrough port 400 and is manipulated to engage first foot 210 in contactwith side 10S1 while second foot 212 contacts the proximal end 10P ofthe first implant 10, as shown in FIG. 5B. Instrument 200 is then usedto drive first implant 10 transversely toward the median of the discspace and potentially at least partially across the median 408 of thedisc space 406, as shown in FIG. 5B. The first side impactor instrument200 is then withdrawn from contact with the first implant 10 and fromthe surgical working space.

The second side impactor instrument 300 is then inserted, working endfirst, through the port 400 and into the disc space. Knob 312 isinserted into and engaged with the proximal most opening 28 on side 10S1and foot 310 is engaged in contact with side 10S1. Instrument 300 is themanipulated to further transversely drive first implant 10 into thedesired position on the opposite side (opposite to the side of the port400 leading into the first side of the disc space) of the disc space406, as shown in FIG. 5C. Because the working end of instrument 300 isoriented at a greater angle to the longitudinal axis of the instrument300, relative to the angle that the working end of instrument 200 isangled to the longitudinal axis of instrument 200, this enables thesurgeon to manipulate the shaft 302 at a greater angle relative to theanterior-posterior direction, which is required in order to translatethe first implant 10 further away from the median of the disk space, ascan be seen by comparing the angle of shaft 302 and median 408 in FIG.5C, to the angle of shaft 202 and median 408 in FIG. 5B. Alternative tothe procedure described above, the placement of the first implant 10 canbe performed without use of first side impactor instrument 200, i.e., byusing instrument 300 immediately after placement by instrument 100.However, this alternative procedure would be more cumbersome than thatperformed using all three instruments 100, 200, 300.

Once the first implant 10 has been positioned on the side of the discspace 406 opposite to the side that it was initially inserted into andis oriented as desired, instrument 300 is removed from contact withfirst implant 10 and withdrawn from the surgical space. Beforeimplanting the second implant, the anterior aspect of the disc space onthe side of the port 400 can be further filled with graft material 402as desired. Also, the space between the first implant 10 and thelocation where the second implant 10 is to be place can be filled withgraft material 402 at this time.

Next, the second implant 10 is inserted using an inserter instrument inthe manner described above. Importantly however, the second implant 10has an orientation that is flipped relative to the first implant.Specifically, prior to insertion, it must be confirmed that the side10S2 having relatively less height: is oriented so that it is lateral ofthe side 10S1 that is non-tapered and has greater height. Thisorientation is better conforms the second implant 10 to the concavity ofthe end plates of the vertebrae that contact the implant on both top andbottom. Likewise, since the shorter side 10S2 of the first implant 10has now been positioned lateral to the taller side 10S1, it also betterconforms to the concavity of the end plates of the vertebrae, and bothimplants 10, 10 therefore exhibit improved load sharing, relative toother implants that have both sides of equal height. Also, in theanterior-posterior direction, the top and bottom surfaces 10T, 10B ofboth implants 10 are convex, and thereby better conform to the concavityof the respective endplates that they support, which also results inimproved distribution of load over the implants 10.

Once the second implant 10 has been positioned as desired, like shown inFIG. 5D, instrument 100 is detached from the second implant 10 andremoved from the surgical space, in the same manner as described abovewith regard to the first implant 10. Additional graft material 402 canbe placed in between the two implants 10, as it is easier to pack graftmaterial 402 in this area after the second implant 10 is placed. Thisgives additional stability to the construct and will encourage ahoneycomb of bone graft healing.

FIG. 5E shows both implants 10 in their desired positions andorientation, after completion of any additional graft material 402packing and after removal of all instruments. The positions of theimplants can be checked at this time to ensure they are as desired, suchas by using an image intensifier and/or fluoroscopy. When the positionsare confirmed as satisfactory, the distraction of the vertebrae isremoved and final compression is applied according to known techniques.Once compression is complete, final tightening of pedicle screws isperformed, also according to known techniques, and the patient is closedaccording to known techniques.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, material, composition of matter, process, processstep or steps, to the objective, spirit and scope of the presentinvention. All such modifications are intended to be within the scope ofthe claims appended hereto.

1-22. (canceled)
 23. A unilateral method of inserting first and secondinterbody implants, said method comprising: creating an interbody porton one side of the spinal column, while maintaining structures of thespinal column and the lumbar musculoligamentous complex on an oppositeside of the spinal column relative to the port, intact; removing discmaterial through an incision in an annulus fibrosus of a disc incommunication with the port and through the port; inserting the firstinterbody implant through the port and into the disc space, wherein thefirst interbody implant has a first distal end portion, a first proximalend portion and first and second sides extending between said firstdistal end portion and said first proximal end portion, wherein a heightof said first interbody implant on said first side is less than a heightof said interbody implant on said second side, and wherein said firstinterbody implant is inserted such that said first side is mediallyplaced and said second side is laterally placed on a first side of thedisc space; driving the first interbody implant from a location in thedisc space on the first side, over the median of the disc space and intoa position in the disc space on a second side of the disc space, suchthat, as a result, the first side is laterally placed and the secondside is medially placed on the second side of the disc; and insertingthe second interbody implant through the port and into the disc space onthe first side of the disc space, wherein the second interbody implanthas a second distal end portion, a second proximal end portion and thirdand fourth sides extending between said second distal end portion andsaid second proximal end portion, wherein a height of said secondinterbody implant on said third side is less than a height of saidsecond interbody implant on said fourth side, and wherein said secondinterbody implant is inserted such that said fourth side is mediallyplaced and said third side is laterally placed on a first side of thedisc space.
 24. The method of claim 23, wherein said first and secondinterbody implants are each substantially trapezoidal-shaped in a crosssection taken normal to a longitudinal axis thereof.
 25. The method ofclaim 23, further comprising distracting the disc space prior to saidinserting steps, by applying distraction forces to vertebrae adjacentthe disc space.
 26. The method of claim 23, further comprising packingeach said interbody implant, prior to said inserting, with a materialthat encourages bone ingrowth.
 27. The method of claim 23, furthercomprising packing a space between said interbody implants, afterinsertion thereof, to encourage a honeycomb pattern of bone ingrowthinto the disc space.